Inside this Article

The PV array placement left room for a solar hot water collector. Note the vertical riser of the geyser pump, a characteristic of the Sunnovations system.

Although this Washington, DC, townhouse has a fairly small, flat roof, it still accommodates both PV and SHW systems.

The vertical part is the geyser pump and the horizontal is the overflow reservoir, which prevents overheating of the heat-transfer fluid.

This concept model has clear glass to view the geyser’s pumping action.

A new Bradford White solar hot water storage tank also provides backup heating, saving space in an already-crowded basement.

A side view of the top of the tank showing the thermometer that measures the tank’s output temperature (the nearest copper pipe riser). Above it is the Honeywell adjustable mixing valve. The pink electrical cable is the 240 VAC electricity for backup water heating. The two twisted pair wires in the background connect to unused sensors (for active, not passive, systems) in the Bradford White tank.

Solar-heated HTF coming into the storage tank (top gauge). The system pressure at the collectors ranges from 28 mm of mercury (vacuum) to 0 (ambient pressure) and depends on the insolation, ambient temperature, and temperature of the fluid returning from the heat exchanger. The gauge at the tank shows a higher pressure, as it includes head pressure (0.43 psi per vertical foot).

The chimney was removed and capped at roof level so it would not shade the PV modules

The old flue is now the chase for the foam-insulated PEX tubing going to and from the SHW collector.

The collector has quite a presence on the modest-sized townhouse’s rooftop.

Beginner

Performance

My system does not yet have an active monitoring system to be able to quantitatively track performance. However, I can share some observations. On sunny days, the HTF going into the storage tank is about 140°F. My summer gas consumption fell from an average of 6.6 therms per month to 0.6 therms (91% less), as it is now just used for cooking.

To get a quantitative sense of system efficiencies, it is useful to compare SRCC ratings for similar systems. The “SHW System Comparison” table (opposite page) depicts the best available approximations of three configurations: a Sunnovations geyser pump system with an AET collector; a geyser pump system with Kioto collectors; and a comparable active pump system with an AET collector.

While this SRCC OG-300 comparative analysis is interesting to technical types, it is not the most appropriate metric to evaluate SHW systems. Most interesting to the consumer is whole-system cost-effectiveness—measured in levelized dollars per kBtu—which is more appropriate, since it also factors in maintenance costs over the system’s life. PEX rather than copper pipe means simpler and less expensive installation costs. No moving parts likely means fewer service calls. Lower—but hot enough—operation means no potential HTF overheating.

The Bottom Lines

I tend to have an early-adopter personality (not among the very first, but ahead of most everyone else), so it’s no surprise that I chose to be one of the first to have a Sunnovations geyser pump when it came time to invest in an SHW system. Although its self-pumped system goes against the grain of current conventional SHW systems by operating at significantly lower temperatures and pressures, moving parts and electronics can fail, and I favor systems without them. I also don’t like having to periodically change out “cooked” HTF.

I was willing to accept a lower total system performance for a passive, rather than active, system (see “Comparison” table). The production penalty (assuming we use every Btu of heat produced) for this particular system would be 19% less hot water than for a comparable active system. Given the significantly lower installation costs (PEX, etc.) and lower expected operating costs, the lower cost made the 19% production penalty worth it.

Now it turns out that the theoretical production penalty for using a Sunnovations passive system in my area (it varies based on the amount of annual insolation) need only be 4% for Washington, DC. Since our installation in December 2011, Kioto collectors are now available in North America. The Kioto collectors have a narrower riser diameter, which make them a more optimum fit with the Sunnovations geyser pump. They are also less expensive than AET collectors.

When one runs the numbers on these same three system configurations as if they were in Albuquerque, New Mexico (see table), it turns out the production penalty for my configuration over an the active system would be 21%. If the Sunnovation Kioto system were used, that penalty would be reduced to 8%.

Will the Sunnovation geyser pump go the distance? Did I make the right choice? I think I did, but only time, data, and experience will tell.

Access

Andy Kerr is a frequent contributor to Home Power and a renewable energy and efficiency blogger (andykerr.net). He splits his time between Ashland, Oregon, and Washington, DC.

Comments (7)

REinMT,
Although it is more costly per unit of heat, I chose electric over gas because:
(1) I avoided having to spend $1200 installing a flu liner in the chimney to be able to continue with gas hot water backup. Having installed a new very high efficiency gas furnace with direct vent to outside wall meant that the waste heat from the aperiodic use of the water heater wouldn't be enough to keep the chimney from rotting from the inside out due to moisture buildup.
(2) I produce 70% of my electricity from PV panels on the roof and will be reconfiguring the existing panels and adding more so when the sun doesn't shine on my SHW system, it previously did on my PV system and my electricity is fossil fuel-free.
I'm sure my electricity consumption has gone up with the added load, but not that I've noticed on the bill.

Andy,
You mentioned tracking performance and your observations. Forgive me if I didn't pick up on this is in the article, but you detailed the reduction in gas consumption after the system was installed but omitted the increase (if any) in electricity consumed by the back-up water heater. Are you grid-tied? Of course gas consumption will decrease because you removed the gas water heater - but has purchased electricity increased at all to account for domestic water heating? Thanks

The Sunnovation Geyser Pump is the only "self-pumped" device certified by the Solar Rating and Certification Corporation (SRCC), the de facto industry standard for rating solar hot water systems. The Copper Cricket is no longer manufactured and I discuss its pros and cons in my article. You might be able to find one used, but who knows what shape it would be in internally. Duplicating the Copper Cricket or the Geyser Pump would be very difficult, if not also patent-infringing on the latter.

Andy
Thanks for your prompt response. They do not sell directly or through distributors, only their installers. I have taken (and passed) the NABCEP Solar Thermal Entry Level exam and am in the process of constructing an Ultra Green Demo Building Project. I prefer to do all my own work. Is there any one else selling a similar product? You mention a Copper Cricket in your article, can that device be duplicated?
Thanks

The installer was Solar Energy Services (solarsaves.net), which services the greater Washington, DC area. You can contact Sunnovations(.com) to see if they would sell you their geyser pump directly, but I think their business model is to work through installers that they certify.

Andy
I have a couple of questions about the geyser pump system.
Did you install the system yourself?
If so, where did you purchase components?
Where can I find individual component prices so I can make a rational comparison as to whether this system would suit my needs and budget?
Thanks